Multi-instrument setup (discrete controllers)

While platforms accepts multiple instruments, the role of them mostly consist in requiring a connection, possibly uploading some parameters during initialization.

However, the active role is usually performed by a single instrument, that will be responsible for playing pulses, the Controller. This is not truly a requirement, since the situation of multiple Controllers is already accounted for: https://github.com/qiboteam/qibolab/blob/f335e4d37376c973ea8372b6c95905245409fe71/src/qibolab/platform/platform.py#L168-L174

However, notice that this is happening sequentially, playing the same sequence on many instruments, and acquiring a result from each of them. This could even be enough, since:

all the instruments could just parse the full sequence, and record the part they are responsible for
one instrument (true or fake) should be responsible to coordinate, and trigger the beginning of the experiment on all the others with its play
only the main instrument will return actual results, possibly merging all the components

It could be more explicit and helpful if:

the role of this coordinator were suggested by Qibolab's Platform layout, if needed
if possible, the platform itself should act as coordinator
- first uploading the sequence to all the actively involved instruments (e.g. instrument.upload(sequence), instead of instrument.play(...))
- then triggering the experiment start
finally, it should be possible to recombine the results before providing them to the users

An example setup, that is currently non-trivial to support, is the case where the pulses on different channels are played by different instruments and acquired by a separate acquisition card, without an internal clustering structure. Qibolab should provide this structure, or an easy-as-possible way to implement it.

qiboteam / qibolab

Multi-instrument setup (discrete controllers) #918